The present invention relates generally to sealing mechanisms, and more particularly to seal rings having application to valves.
The present invention is an improvement over prior art high-performance sealing mechanisms which have attempted to provide leak proof sealing and which continue to function even in the event of and following high temperature situations or fire. The need for such sealing mechanisms is particularly acute in the petroleum industry, where petroleum drilling and processing are subject, on occasion, to very high temperatures or even combustion of the material handled.
A prior art invention of Simmons et al, U.S. Pat. No. 4,113,268, provides a fire proof, bubble-tight sealing mechanism which utilizes a two stage arrangement. A soft primary seal, for example of Teflon, is inserted in the rib of a metal seal ring for contact with the complementary surface of a closure member. The Teflon material, extending radially inward beyond the metal rib, provides a bubble-tight seal under normal conditions. In the event of fire, the Teflon is destroyed. Subsequently, the metal rib of the seal ring dynamically moves into position to form a secondary or metal to metal seal.
While the Simmons et al invention was a major advance in the art, which provided an unprecedented quality of sealing and fire safety in a butterfly valve, certain drawbacks nevertheless exist. The primary seal necessitates the machining of the metal and the insertion of a soft material into the metal rib of the seal ring, the insertion thereof which is a relatively difficult and expensive manufacturing procedure.
Benware, in U.S. Pat. No. 3,642,248, discloses a valve sealing mechanism which discloses the type of dynamic sealing utilized in a preferred embodiment of the present invention. In Benware, the seal ring is fitted within a circumferential groove of a body member. A portion of the seal ring extends out of the groove, radially inward, for mating engagement with a closure member or disk. The seal ring is arranged within the groove for moveable adjustment in response to the pressure of the system.
The seal ring of Benware, in a preferred embodiment, has a backing ring which is held within the groove, beneath the seal ring. This backing ring provides a preloaded sealing force for the side-sealing of the seal ring with the walls of the groove.
The seal ring of Benware is preferably constructed of a soft material such as Teflon. However, a second embodiment discloses a metal seal ring. In the latter, a pair of inclined surfaces at the sides of the seal ring abut the lateral sides of the groove and are preloaded by being of a slightly greater dimension than the width of the groove. The front of the seal ring is curved slightly and concavely in relation to the disk surface. This causes the upstream and downstream edges of the seating surface of the seal ring to bite against the disk surface when the seal ring is pushed against the disk.
This metal seal ring of Benware has proved unsatisfactory. Although the seal ring is constructed of metal for fire safe performance, the metal to metal contact does not provide the desired quality and reliability of sealing for the desired use of such valves.